Call devices

Details Call devices Call devices

H - Electricity

04

M

379/66, 379/80,

H04M 1/74 (2006.01) H04M 9/08 (2006.01) H04M 11/04 (2006.01)

Patent

CA 1274330

ABSTRACT CALL DEVICES A call device for use by elderly people or for use in situations having a high ambient noise level is provided with a voice operated switch in which the effects of leakage signals, which appear in the receive channel due to leakage across a hybrid circuit (D1) from the send channel, are cancelled by a signal derived by rectifying and integrating send signals in the send channel. Receive signals Vr, received from a transmission line to which the call device is connected by the hybrid circuit, are rectified and integrated to produce a control voltage. A comparator (D4) generates a control signal when the control voltage exceeds a reference voltage to enable a switch (R) in the receive channel and disable a switch (S) in the send channel. This enables a receive signal to override any send signal which may arise due to ambient noise and permits use of a sensitive send channel and high volume sound from a loudspeaker (L/S) in the receive channel.

546438

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